1. Field of the Invention
The present invention relates to a hydraulic reservoir and, more particularly, to a hydraulic fluid reservoir formed by rotational molding with one or more integral extended depth return lines.
2. Brief Description of the Prior Art
Rotational molding, or rotomolding, is a well-known method of forming objects from a plastic resin. It is often used for complex shapes including tanks and reservoirs. Various types of plastic resin can be used, such as polyethylenes, plastisols, nylons, fluoropolymers, polypropylenes, polyurethanes, and other suitable materials.
In general, a mold is loaded with a plastic resin and heated in an oven. As the mold is heated, the mold is rotated about two or even three, axes at a low speed. The heat melts the plastic resin inside the mold and melted resin coats the interior surface of the mold. The mold is then gradually cooled using air or water and the resolidified plastic resin, which has assumed the shape of the interior walls of the mold, is removed from the mold. This process differs from injection molding in that the plastic resin is not pressurized (other than atmospheric pressure).
As shown in U.S. Pat. No. 5,285,923, it is occasionally necessary to insert objects made of a material other than plastic resin into the object to be formed, such as brass inserts molded into a polyethylene material. U.S. Pat. Nos. 3,364,292; 4,023,257; 4,143,193; 4,847,028; and 5,911,938 also discuss rotomolding with inserts added to the molded product. All of the above-cited references are incorporated herein by reference.
As noted in the above-cited prior art, rotomolding is well-suited for forming a plastic tank or reservoir structure. Such tanks are often used as hydraulic reservoirs for hydraulic systems, such as used in heavy machinery, including cranes, backhoes, demolition shears, bulldozers, and the like. In hydraulic systems, it is important to keep the hydraulic fluid free of debris. Consequently, filtering elements have been incorporated in the hydraulic systems to filter debris from the hydraulic fluid.
It is an object of the present invention to provide a rotomolded hydraulic reservoir with at least one extended length return line for the hydraulic reservoir. It is a further object of the present invention to provide a rotomolded hydraulic reservoir with integral filter bowl having an extended integral filter container with a coupling insert. It is another object of the present invention to provide a rotomolded hydraulic reservoir with an improved baffle and a second extended depth fluid return. It is another object of the present invention to provide a hydraulic reservoir which is economically manufactured. It is a further object of the present invention to provide an effective, easily replaceable filter element for a hydraulic reservoir.
The above objects are achieved with a rotomolded hydraulic reservoir having at least one extended length return line according to the present invention. The hydraulic reservoir is a one-piece tank structure. Specifically, the hydraulic reservoir includes a plastic container body defining a container cavity for receiving the hydraulic fluid. The container body may form a filter cavity in fluid communication with the container cavity. A filter element coupling insert, such as a machined metallic bushing, may be molded in the container body adjacent the filter cavity. The insert defines an opening, specifically an internal bore, providing the communication between the container cavity and the filter cavity. A removable filter element is positioned within the filter cavity and coupled to the insert. The removable filter element seals to the exterior of the insert.
The fluid communication provided between the filter cavity and the container cavity is provided to extend to a level below the normal fluid level in the hydraulic reservoir. Additionally, a second fluid return communicating with the container cavity may be provided in one embodiment of the present invention with the second fluid return including an integral metallic coupling insert. The second fluid return may be provided with a fluid communication with the container cavity at a level lower than the normal fluid level within the container cavity. A normal fluid level for a hydraulic reservoir varies between rest and operating conditions. Although the fluid level in a hydraulic reservoir is dynamic, the term normal fluid level is a specific defined range unique to a given hydraulic reservoir and a given application. The provision of the return lines to a level below the normal fluid level will prevent foaming in the fluid within the container cavity.
These and other advantages of the present invention will be clarified in the description of the preferred embodiments taken together with the attached drawings in which like reference numerals represent like elements throughout.